This will be the first Gordon Research Confernce on MOTILE AND CONTRACTILE SYSTEMS. The work to be presented will start with the very recent discoveries on the role of ATP hydrolysis in actin polymerization and the regulation of actin polymerization by actin-binding proteins such as profilin and gelsolin. Mechanisms of regulation of myosin filament formation and actomyosin ATPase activity will be discussed with emphasis on the role of heavy chain phosphorylation (discovered in amoeba but now known to occur in mammalian non-muscle and cardiac muscle cells) and the role of the Ca/calmodulin-binding protein caldesmon. For the first time, sequence data (at the DNA level) are available for non-muscle myosin heavy chains and these data will be discussed in comparison to the sequences of muscle myosin heavy chains. Recent information on the localization of the sites on actin and myosin that are involved in their interaction will be presented as will interesting new data on the ATP-binding site of muscle and non-muscle myosins. The organization of the cytoskeleton of non-muscle cells will be discussed including its dynamic regulation during platelet activation and the effects of actin mutants on cytoskeletal organization and function of yeast and dictyostelium. Genes encoding contractile proteins are often members of multigene families coding for multiple protein isoforms that are expressed in a tissue-specific and developmental-stage specific manner. Recent studies focus on the differntial regulation of expression of individual genes within a multigene family and the coordinate expression of cytoskeleton protein genes between different multigene families. Motile systems involving microtubules will be discussed: both the microtubule-dynein system and the very exciting, newly discovered microtubule-kinesin system that seems to be involved in axonal transport. The final session will cover the role of second messengers (cyclic nucleotides, inositol triphosphate and diacylglycerol) in cell motillity, cell shape changes and muscle contraction. The Conference will include approximately 25 formal presentations by invited speakers with major emphasis on discussion by invited and uninvited participants. The latter, especially, will be encouraged to present posters of their work and one session will be devoted to discussion of the posters. This will be the first meeting of scientists involved in so many different yet closely related aspects of the motile and contractile systems.